| PAARL WASTEWATER TREATMENT WORKS
The first wastewater treatment works at Paarl was constructed in the 1930’s and consisted of a biofiltration system for domestic wastewater and a series of evaporation ponds for industrial wastewater. This works was upgraded in 1957, which was followed by further extension to the maturation ponds in 1960, for further treatment of the effluent from the works before it is discharged into the Berg River. Later, the capacity was supplemented by installing floating aerators to the first maturation ponds. This was later followed by the installation of larger aerators and the construction of clarifiers and sludge return facilities to convert the aerated ponds to an activated sludge system.
The current extension increases the capacity of the works to 35 Ml/d. The process formalizes the activated sludge system that developed over time and makes provision for biological phosphate and nitrogen removal as well as for lining the bioreactor to eliminate the risk of groundwater pollution (which could ultimately end up in the Berg River). The new biological reactor is being constructed in the original aerated pond.
The raw wastewater arrives at the site in two main streams, one predominantly from industrial origin and the other predominantly from domestic origin. The configuration of the works makes provision for the industrial stream, plus some of the domestic flow, to be diverted through the biofilter works (the original works) while the balance of the domestic flow bypasses this works. The "bypass flow" plus the wastewater treated in the biofilter works is again combined to be treated at the activated sludge works. |
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The activated sludge works consist of two streams, each with a capacity of 17,5 Ml/d. Limitations in the availability of capital necessitated that the works be expanded in two phases. Currently the first stream with a capacity of 17,5 Ml/d (17 500 m3/d) is being commissioned. The “circular pond” to the west of the new bioreactor served as a temporary biological reactor whilst the new reactor is being constructed. This pond will still provide additional bioreactor capacity until the second phase has been commissioned.
According to the current master plan for wastewater treatment in the Drakenstein area, no further extensions will be constructed at this site.
The most important statistics of the extended works are given below:
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Design Parameters |
|
Parameter |
Activated Sludge Works |
Total Works |
|
COD (t/d) |
25,8 |
36 |
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TKN (t/d) |
1,8 |
2,3 |
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Total P (t/d) |
0,3 |
0,6 |
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Installed power for aeration (kW) |
900 |
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Statistics of Full Activated Sludge Works |
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Hydraulic Load – ADWF |
35 Ml/d |
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Activated Sludge Volume |
2 x 26 250m3 = 52 500 m3 |
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Anaerobic |
2 x 4 773 m3 = 9 546 m3 |
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Anoxic |
2 x 10 739 m3 = 21 477 m3 |
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Aerobic |
2 x 10 739 m3 = 21 477 m3 |
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Design Sludge Age |
20 days |
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MLSS at Design Capacity |
3 500mg/l |
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Clarifiers |
4 x 33m diameter | |
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